Abstract : The sequence of events in the retinal rod leading to a nerve impulse can be summarized as follows: The absorption of a quantum results in an excited state involving the retinene-protein bond. The absorbed energy may migrate by exciton transfer to the site of the reaction sequence which results in membrane activation. This second system requires only an initial activation before proceeding spontaneously. After the energy transfer the retinene is detached from its protein bond and appears as free retinene for a brief interval before it reacts secondarily to form amino bonds with substances present in the rod or in solution. (Author)